https://www.getmailbird.com/what-spf-resources-are-available-now-that-openspf-org-is-gone/

According to the above URL openspf.org disappeared in early 2019.

Jun  7 05:18:38 itmustbe postfix/policy-spf[2667136]: Policy action=550 Please see http://www.openspf.org/Why?s=mfrom;id=XXXX%40XXXXXXX.XXXXX.net;ip=999.99.999.99;r=luv.asn.au

Currently messages like the above are being logged and given in bounce
messages.  It should either direct to another site that gives the same
results as openspf.org used to give, or it should give a human readable
message like "Please note that IP 999.99.999.99 is not allowed to send mail
on behalf of XXXX@XXXXXXX.XXXXX.net due to SPF policy".